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Quantification of Raindrop Kinetic Energy for Improved Prediction of Splash-Dispersed Pathogens

First and third authors: IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, North Somerset BS41 9AF, United Kingdom; second author: ADAS High Mowthorpe, Duggleby, Malton, North Yorkshire YO17 8BP, United Kingdom; fourth author: Silsoe Research Institute, Wrest Park, Silsoe, Bedford MK45 4HS, United Kingdom; and fifth author: IACR-Rothamsted, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom

An electronic sensor, based on a piezoelectric transducer, was tested in the laboratory using simulated raindrops, and in natural rainfall. Data were also collected for splash dispersal using tracer dyes in laboratory experiments and the Long Ashton splashmeter in field experiments. Droplets impacting on sensor produce sound waves that are detected by an omnidirectional microphone sealed within an acoustic chamber. An electrical charge, proportional to the sound wave, is produced by the microphone and is converted to a categorical scale and then stored to provide an accumulation of impacts over a specified period of time. Calibration of the sensor was done using single-droplet impacts of known mass and impacting velocity. A linear relationship was shown between the categorical scale and the kinetic energy of impacting droplets (adjusted r² = 0.99). The best relationship fitted between splash dispersal from dye cup, and kinetic energy was a second-order polynomial (adjusted r² > 0.99). Splash height, recorded by the Long Ashton splashmeter during 41 natural rainfall events, was correlated closely with sensor output (adjusted r² = 0.87). Our studies indicate that the sensor provides quantitative data which could be incorporated into disease management systems to provide estimates of inoculum dispersal gradients within crop canopies.

Additional keywords: environmental epidemiology, meteorology, quantitative epidemiology, Septoria tritici, spore dispersal.